False-colour transmission electron micrograph of the flagellate bacterium Bacillus thuringiensis. The bacterium is an important insect pathogen, causing toxaemia and septicemia in the larvae of butterflies and moths. Preparations of B. thuringiensis are commercially produced for use as microbial insecticides. They contain a mixture of bacterial spores and toxic crystals and are applied to crops as sprays or dusts. They are harmless to higher animals, including man (and even to beneficial insects such as honeybees) and can be used on crops close to the harvest period when chemical insecticides are no longer allowed.